The present invention is directed to a reactor, a retained catalyst structure, and a method for improving decomposition of polysulfides and removal of hydrogen sulfide in liquid sulfur. More specifically, the reactor, the retained catalyst structure, and the method involve a catalyst for improving simultaneous decomposition of hydrogen polysulfides to hydrogen sulfide and removal of hydrogen sulfide with an inert gas or a low oxygen-containing inert gas.
Generally, the Claus process is used to recover sulfur from hazardous waste gas streams containing hydrogen sulfide gas produced during refining of petroleum products, natural gas processing and gasification. The Claus process involves partially combusting hydrogen sulfide in air, oxygen, or oxygen-enriched air to produce sulfur dioxide. Sulfur dioxide then reacts with remaining hydrogen sulfide to produce sulfur. Sulfur is recovered from the Claus process in a liquid form. Handling of the liquid sulfur produced from the Claus process can be difficult due to the polysulfides and dissolved hydrogen sulfide gas present therein. The polysulfides degrade slowly, thereby producing toxic, odorous and highly flammable hydrogen sulfide gas. A large portion of the hydrogen sulfide gas is retained by liquid sulfur as a dissolved gas. In untreated liquid sulfur, a small portion of the hydrogen sulfide gas is released slowly into the environment. The gradual degradation of the polysulfides and the release of the dissolved hydrogen sulfide gas during storage and transportation involve substantial health, safety and environmental risks and may result in fire. The toxicity of hydrogen sulfide involves substantial safety risks.
Known processes have been developed to mitigate issues with the gradual release of hydrogen sulfide gas. In general, the processes involve accelerated decomposition of polysulfides and removal of dissolved hydrogen sulfide from liquid sulfur.
One such process is captured in U.S. Pat. No. 4,729,887; hereby incorporated by reference. The U.S. Pat. No. 4,729,887 describes the conversion of hydrogen polysulfides to hydrogen sulfide from a liquid sulfur stream through liquid treatment by a solid particulate catalyst. The hydrogen sulfide is then removed from the liquid stream by a stripping gas. The stripping gas for use in the U.S. Pat. No. 4,729,887 is preferably a non-inert gas containing elemental oxygen or sulfur dioxide. In the U.S. Pat. No. 4,729,887 the liquid sulfur and stripping gas stream flow co-currently upflow through the solid catalyst treatment area. In concurrent flow the stripping gas and liquid sulfur have relatively low contact time with the solid catalyst, potentially requiring recycling the liquid sulfur stream through the solid catalyst many times to effectively convert hydrogen polysulfides and strip out the hydrogen sulfide. Furthermore, infusion of untreated liquid sulfur flow into the solid catalyst treatment area would need to be relatively low compared to the recycling treated liquid sulfur flow, so as to maintain the desired concentration of hydrogen sulfide in the treated liquid sulfur. The upflow configuration may also result in fluidizing the catalyst bed due to similar densities of liquid sulfur and catalyst, causing crushing of the catalyst and contaminating the treated liquid sulfur stream with fine catalyst particles.
A known process for mitigating these issues is described in U.S. Pat. No. 5,632,967, which is hereby incorporated by reference in its entirety. The U.S. Pat. No. 5,632,967 describes a first stream including liquid sulfur containing polysulfides and dissolved hydrogen sulfide and a second stream of oxygen-containing gas being contacted in a reactor (operated under pressure to increase oxygen partial pressure) packed with a mixing device. Specifically, the mixing device is submerged in the first stream including liquid sulfur and the second stream of oxygen-containing gas is bubbled into the first stream including liquid sulfur from the bottom of the reactor. The second stream of oxygen-containing gas oxidizes hydrogen sulfide and polysulfides present in the first stream including liquid sulfur to form sulfur and strip dissolved hydrogen sulfide from the liquid sulfur. The stripped hydrogen sulfide gas is removed from the top of the reactor along with any unused portions of the second stream of oxygen-containing gas. The stripped hydrogen sulfide gas and unused portions of the second stream of oxygen-containing gas may be recycled back to the Claus reactor. The treated first stream including liquid sulfur includes less than about 10 parts per million by weight (ppmw) of combined polysulfides and dissolved hydrogen sulfide gas. The treated first stream including liquid sulfur is removed from the bottom of the reactor, stored as a liquid or solidified, then provided to end users.
The process described in U.S. Pat. No. 5,632,967 may also involve a catalyst in a packed bed of spherical or pelletized catalyst. Catalytic oxidation of hydrogen sulfide and polysulfides in the U.S. Pat. No. 5,632,967 patent occurs when the first stream and the second stream contact in the packed bed. The oxygen containing stripping stream may react with liquid sulfur and dissolved H2S, forming SO2 and moisture. The process described in U.S. Pat. No. 5,632,967 does not include decreasing the combined polysulfides and hydrogen sulfide content in the liquid sulfur to less than 5 ppmw. To meet increased environmental restrictions, a decreased combined polysulfides and hydrogen sulfide content in the liquid sulfur is desired. In addition, improved energy efficiency and operational costs are also desired.
U.S. Pat. No. 6,149,887, which is hereby incorporated by reference in its entirety, discloses a method for removing hydrogen sulfide and hydrogen polysulfide compounds from liquid sulfur by stripping with a gas. U.S. Pat. No. 6,149,887 expressly suggests that use of a catalyst is disfavored. U.S. Pat. No. 6,149,887 suggests that introducing a catalyst to the liquid sulfur and, thereafter, stripping the catalyst from the sulfur can result in several drawbacks. This patent suggests that use of the catalyst may clog portions of the system and/or result in catalyst being present in the removed sulfur.
U.S. patent application Ser. No. 12/692,978, filed Jan. 25, 2010, entitled “A Reactor, a Structured Packing, and a Method for Improving Oxidation of Hydrogen Sulfide or Polysulfides in Liquid Sulfur”, which is hereby incorporated by reference in its entirety, discloses a reactor including a first inlet for a first stream including liquid sulfur containing polysulfides and dissolved hydrogen sulfide, a second inlet for a second stream of oxygen-containing gas, and a structured packing for contacting the first stream and the second stream, the structured packing having a catalyst. The catalyst accelerates the rate of decomposition and oxidation of polysulfides and oxidation of hydrogen sulfide in the liquid sulfur of the first stream with the second stream.
In the Ser. No. 12/692,978 patent application, a catalyst coated packing is employed in order to achieve an accelerated decomposition of H2Sx to H2S, and partial oxidation to elemental sulfur and SO2 and oxidation of hydrogen sulfide to SO2 and elemental sulfur. The converted H2S produced by decomposition of polysulfides is in turn oxidized to SO2 and to elemental sulfur. Elemental sulfur is also produced by the reaction of H2S with SO2. An unwanted product from the reaction of H2S and O2 is H2O, which could lead to corrosion of internal metal surfaces. The Ser. No. 12/692,978 patent application utilizes an oxygen containing stream at above atmospheric pressure.
A method and system for further decreasing combined polysulfides and hydrogen sulfide content in liquid sulfur, a method and system for decreasing combined polysulfides and hydrogen sulfide content in liquid sulfur utilizing inert or low oxygen-containing stream, and/or a method and system for decreasing combined polysulfides and hydrogen sulfide content in liquid sulfur capable of operation at low or high pressures having increased handling options for removed gases is desired in the art.